Aerogel is a solid material with a porosity of over 95%. Although aerogel is lightweight, it has superior mechanical strength. Further, aerogel features low thermal conductivity, low acoustic conduction speed and low permittivity. Aerogel can be used to produce thermal insulating materials, sound insulating materials, electrical insulating materials and absorptive materials. Therefore, aerogel is a promising material, and many researchers have been devoted to studying and improving aerogel.
A US Patent No. US 2009/0123985 disclosed a method for fabricating an aerogel and applications thereof to biocomposite materials, wherein different amounts of different ion solutions are used to modify the pore size and specific surface area of the aerogel. The aero fabricated thereby is used to produce organic/inorganic composite materials and biocomposite materials, which are to be used as materials for absorption, catalysis, separation, and medicine release. The ion solutions used by the prior art are non-volatile, inflammable, easy to prepare, easy to separate and easy to recycle. Therefore, the process of the prior art meets the global trend of environmental protection. Further, the prior art does not adopt the traditional supercritical fluid process to fabricate aerogel. Therefore, the prior art is free from the complicated procedures of the traditional supercritical fluid process and exempted from the risk of explosion of the traditional supercritical fluid process.
The safety of aerogel is dependent on the source materials thereof. If the source materials have toxics or carcinogens, the aerogel fabricated therefrom will be toxic or carcinogenic also. Polyvinyl alcohol (PVA) does not carry significant toxicity and is usually used as the source material of aerogel. The aerogel fabricated with small-molecule PVA lacks industrial applicability because it is likely to dissolve in water. Therefore, aerogel is usually fabricated with large-molecule PVA. However, large-molecule PVA is hard to dissolve in water. Thus, large-molecule PVA is usually dissolved in an organic solvent, such as toluene, in fabricating aerogel. While toluene is used as the organic solvent, the aerogel fabrication process must involve waste liquid treatment. Further, the aerogel fabrication apparatuses need chilling because the melting point of toluene is very low (−95° C.). Therefore, the traditional aerogel technology still has room to improve because of the problems of waste liquid treatment and high energy consumption.